1. Field of the Invention
This invention relates generally to a rail fastener and more particularly to a fastener for holding a rail onto a support structure which provides improved structural integrity between the rail and the support structure and improved conditions for precast manufacturing sections of railroad track with rigid assembly datum surfaces.
2. Prior Art
There are some different types of rail fasteners used on railroad tracks and described in patent literature.
Generally, they may be divided on three groups. The first is the simplest one which introduces the rail fasteners which consist of simple spikes or of special plates with spikes. The second group represents so-called direct fixation rail fasteners. For example, fasteners according U.S. Pat. Nos. 4,382,547; 4,260,105 3,858,804; and 4,917,295. To the third group relate tie plates with spring clips. For example, U.S. Pat. Nos. 4,307,837; 4,407,663.
Presently the trend in manufacturing of railroad tracks is to precast the second and the third groups of fasteners. Though these two groups are different in design, both of them have common problems. Any of known fasteners has a base plate secured to the support structure. This plate has a central recessed area adapted to receive the lower end of rail on its upper surface. In the direct fixation design rail fastener the rail is secured to the base plate by different types of hold-down plates. In the tie plates of a spring clip rail fastener the spring clips press the rail to the base plate.
As rails cannot be strictly straight and the geometry of the track isn't always straight, the recess in the base plate has more width than the width of lower end of rail. This difference in width permits placement of the rail into numbers of recesses of base plates secured to the support structures in advance. So, after assembly there are different lateral clearances in every connection of rail to base plate.
The problem is that rails in all known fasteners are permitted to move laterally. So, when a vehicle runs over a rail the lateral shear forces appear and rail moves in its clearance with impact to the vertical walls of the recesses bearing the rail. This impact produces sound and gives rise wear of the walls. As a result, the clearance becomes greater over time and the gage of the track will not be maintained. This may cause the vehicle to lose contact with the rail. Also, when rail moves, the car running over it moves laterally with rail and begins swinging.
The second problem is that the gage of the track is maintained not directly based on the rail. For this purpose they use centers of the recesses on the base plates. This method cannot be very precise, because it depends of many problems which depend of quality of manufacturing and assembly.
The third problem is that such types of tie plates cannot be used on the curve section of the track, because the recesses are straight.
One more problem is that in all prior known fasteners the lateral shear forces eventually takes up the bolt which secures the tie plate to the support structure. This cannot be the best solution because the bolt tends to be selfloosening and to prevent this additional members are needed that are costly to manufacture. As to the tie plates with spring clips, the spring clip requires special equipment for its production and a special device for assembly of the spring clip with the plate and rail because the springs have a high spring constant.